1. Field of the Invention
The present invention relates fluid level indicators. More particularly, the present invention relates to fluid level indicators useful in conjunction with rigid containers having flexible liners for storing or processing liquids or other fluid materials.
2. Description of the Related Art
Storage and processing containers are in widespread use in various industries and other endeavors. Many of these are used to contain liquids and other flowable bulk materials, such as powders and granular materials. While containing many types of fluid materials, it is preferable to line the container with a polymeric membrane so that the bulk material is either impermeably contained in a suitable polymeric material, or to insure that the bulk materials does not contact the container itself. For example, in the case of pharmaceutical and food grade materials, a polymeric liner, such as PVC or polypropylene, may be used to maintain the purity and cleanliness of the bulk material. In other instances, the bulk material may react with a storage container itself, so a polymeric liner is used to prevent such reactions.
Various fluid level indicators are known and used with liquids and other bulk fluid materials. Most level indicators sense fluid level using some form of direct contact with the contained bulk material. For example, the classic floating level indicator is commonly used in fuel tanks Another classic example is the liquid sight gauge, where the contained liquid level is visually presented through a transparent portion of the gauge. Other fluid level indicators use more sophisticated detection techniques, including acoustic detection, proximity detection, mass, pressure and so forth. However, these more sophisticated techniques are generally complex, expensive, and somewhat unreliable over time unless maintained by skilled technicians.
In the case where an impermeable liner is placed between a rigid container and a bulk fluid material being stored or processed therein, the challenges associated with the task of fluid level indication are increased. The operation of devices such as float gauges, sight glasses, and other direct contact system are interfered with by the liner membrane. Plumbing connections are more challenging, and would reduce system reliability and performance if attempted. Electronic fluid level detection devices can be interfered with as well. Thus it can be appreciated that there is a need in the art for an apparatus for indicating the fluid level in a lined container that overcomes the challenges associated with prior art designs.